Methods and materials for packaging fibrous materials are known. Cellulose acetate tow, for example, is a fibrous material that is typically compressed into a bale for packaging, storage and shipment. Cellulose acetate tow is a continuous band or bundle of cellulose filaments that may be processed into cigarette filters. Generally, cellulose acetate tow has low bulk density, e.g., approximately 100 kg/m3, and is compressed to increase this bulk density for improved handling and transport efficiency. After being compressed into a bale, cellulose acetate tow exerts an expansion force, which must be effectively controlled in order to maintain the desired bulk density and size for storage and shipment. Packaging materials, such as polyester straps, are typically used to counteract the expansion force of the tow bale and must be able to withstand a significant internal pressure, which may be on the order of up to 35 N/cm2 just prior release of the compressed tow into the packaging. The packaging materials must also be able to sustain an internal force of up to 5 N/cm2 once the tow bale is packaged.
Numerous packaging methods have been suggested by the prior art. U.S. Pat. No. 8,161,716 discloses a packaging method for a filter tow bale including excessively compressing a distance between press bases to a height lower than a desired height of a packaged bale by 50 to 250 mm, more preferably 80 to 200 mm, further preferably 90 to 180 mm, then adjusting the distance between the press bases to the desired height in a packaged or non-packaged state, and then releasing a pressing force applied on a pressed bale.
U.S. Pat. No. 5,732,531 discloses a method for wrapping a bale of compressed, resilient fibers comprising the steps of: providing a reusable bale wrap kit which includes at least two pieces. Each piece, when joined with the other piece, is adapted for substantially enclosing and containing the bale of compressed, resilient fibers. Mushroom and loop fasteners are located along an edge portion of each piece and are adapted for joining the pieces to one another. Uncompressed, resilient fibers are provided. A portion of the uncompressed, resilient fibers are surrounded with the kit. Those fibers are compressed, and the mushroom and loop fasteners are engaged.
U.S. Pat. No. 4,157,754 discloses compressed that fibers, filaments, or cabled tows, which are under an internal pressure of at least 0.2 daN/cm2, are packaged by means of an outer wrapping, an the overlapping areas of the wrapping are held together by means of an adhesive, for instance a neoprene-chloroprene-rubber based adhesive. In this manner, it is possible to eliminate straps, belts or wires which have been conventionally used to hold the package. As shown in FIG. 1, the adhesive is a glue that is applied to the entire overlap area.
GB 1512804 claims a method of preparing and packaging fodder comprising the steps of partially wilting green herbage, inserting a compacted block thereof into a bag or wrapper of impermeable plastics material, hermetically sealing the bag or wrapper against ingress of air and, before or after sealing, providing a non-return valve to allow the contents to exhaust to atmosphere.
AU737531 discloses a multi-layer plastics packaging in the form of a bag for packaging bales of wool, a bag being sealed at one end to form a substantially square bottom for the bale. The structure of the multi-layer coextruded film employed to manufacture the wool bag is carefully designed to obtain the necessary mechanical properties required to withstand the rough handling of wool bales during transportation and storage. The multi-layer film comprises a first layer of high stiffness plastics material forming a core or intermediate layer of the multi-layer film, and second and third layers of high strength plastics material. The desired physical characteristics or mechanical properties of the multi-layer film are achieved using a blend of various density polyethylene plastics materials in each of the first, second and third layers.
AU3302184 claims a woolpack comprising a bag of a non-woven sheet material closed at one end by multiple closure elements disposed to shape a broadly rectangular bottom for the bag when expanded, and closure flaps for closing the other end of the bag. The bag is in the form of a tub flattened into a four layer configuration comprising opposed outer layers which act to sandwich therebetween two folded side gussets of substantially similar width, each gusset extending inwardly from a respective longitudinal edge of the flattened tube with the inner edges of the two gussets extending substantially along the longitudinal centre line of the flattened tube. The multiple closure elements comprise respective mitre seals which connect each layer of each gusset to the adjacent outer layer. Each mitre seal extends diagonally from the centre region of a bottom transverse edge of the tube to a respective longitudinal edge of the tube. The four layers are connected by a further seal which extends across the bottom transverse edge, the arrangement being such that in the expanded bag the four mitre seals each extend from a centre region of said broadly rectangular bottom to the corner portions of said substantially rectangular bottom.
However, these existing packaging methods are complicated, expensive, and may be dangerous. For example, a strap under high pressure may snap during storage or may spring back during opening. Vacuum sealing and heat sealing require additional equipment and the seal must be sufficiently strong to maintain the vacuum or air-tight conditions during storage. Thus, the need exists for improved methods for packaging fibrous material, especially for packaging cellulose acetate tow bales, that are cost effective, uncomplicated, and sufficiently robust so as to withstand the internal pressure of the fibrous material.